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Old 01-06-2013, 09:18 PM   #1
jmfitzgerald
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Default refractometer vs hydrometer readings...

so today was my first use of a new refractometer i got for christmas, and can't seem to get my head around some of the readings... i worked on 2 batches so have numbers from each.

first off, yes i calibrated the new refractometer to room temp and distilled water.

today i put together a new pyment and the numbers were pretty close vs what i see some online calculators predicting. for a starting gravity on the refractometer i read 23.9 Brix, and 1.102 SG on the Hydrometer. via this online calculator http://www.brewersfriend.com/brix-converter/ they are within a couple points of each other... i'd say close enough???

now onto racking a blueberry vanilla melomel off the blueberries, and into a clean carboy, this is where i'm confused, and i checked both readings twice. the refractometer was reading right at 9 Brix and the hydrometer was reading 1.008 which is right where i think it would be. as of a month ago, when i added the second addition of blueberries, it was at 1.004. i was kept on the cooler side, if not too cold, so with the the addition of the blueberries, and maybe the yeasties being too cold, i could see the addition of a couple points and not dropping more.

so the big question. why do the numbers seem to be more consistent with the new batch and seem to be way off and different from each other on the racked melomel????

thanks for any insight!





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Old 01-06-2013, 09:29 PM   #2
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Alcohol will throw off refractometer readings. Some calculators attempt, with varying success, to compensate for this by taking into account the OG (you have to provide this.)



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Old 01-07-2013, 05:34 PM   #3
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so pretty much stick with using a Hydrometer for all reading past the initial SG of the must? for some reason i though using a refractometer was going to be great by just taking a very small samples along the way, but i guess it's not accurate once fermentation starts because of the alcohol? huh.
well thanks.

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Old 01-07-2013, 05:37 PM   #4
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Originally Posted by jmfitzgerald View Post
so pretty much stick with using a Hydrometer for all reading past the initial SG of the must? for some reason i though using a refractometer was going to be great by just taking a very small samples along the way, but i guess it's not accurate once fermentation starts because of the alcohol? huh.
well thanks.
Actually, I bet you can find a webpage that will do all the work for you. As long add you have an OG and SG, you should be fine.
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Old 01-07-2013, 07:02 PM   #5
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Actually, I bet you can find a webpage that will do all the work for you. As long add you have an OG and SG, you should be fine.
Here is one I found with a quick Google search: http://onebeer.net/refractometer.shtml. I use the one built into Beersmith and it seems to do the job. I do occasionally check my adjusted refractometer values against my hydrometer, just to convince myself though.
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Old 01-07-2013, 07:03 PM   #6
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I understood the same as what voltin said i.e. that the alcohol throws off the reading.

The refractometer will give you a good reading from a pure must like honey and water but once the levels of available sugars start to drop then its time for a hydrometer - thats how professional wine makers seem to operate. They test the actual fruit to tell when its ripe and ready for harvest, but once its destemmed and crushed they sample the juice for the SG (well thats how it was explained to me).

Now if its a batch that includes fruit you have to take account of the fruit sugars. There are a number of tables that show the average sugar levels for certain fruit but of course, unless you extract the juice and add it you can only guesstimate it. Because to get an accurate number it would have to be whole or diluted juice whereas guessing how much sugars you add by say adding 3lb of fruit to a gallon of honey and water must would only ever be a guess.

So hence its often better to use a lower gravity must with the fruit ferment dry or step feed. So you either end up at a specific level of dryness (which you'd then modify if you wanted) or you step feed incrementally with honey or extra fruit until the yeast tolerance is exceeded -to your chosen level of sweetness.

Obviously you'd think about the choice of yeast to achieve your aim....

Oh and don't forget, professional makers will know the alcohol content/level exactly, because they or their chosen lab will have access to the kind of kit home brewers can only dream about....... (and in some locations they need accurate figures because that's what they pay tbeir excise duty against)......

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Old 01-07-2013, 09:30 PM   #7
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great thanks! this is all great info, guess i should of researched a bit more before getting the refractometer... but either or, it's another good tool to have, and i learned something new.

where i thought it would be great is checking the gravity along the aging process. i've been doing quite a few small 1 gallon batches, and was thinking less of contamination, oxidation, etc by taking a couple small drops of the mead out vs taking out a big enough sample to float a hydrometer in, then returning that sample. again because of the small batches, or i'd have no mead left and tons of head space in the carboy but i guess i'll keep sanitizing everything all the time and so far so good!

thanks again, these forums are great!

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Old 01-07-2013, 10:56 PM   #8
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I am wondering, has anyone tried measuring the specific gravity of pure honey with a refractometer before? Would that work?

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Old 01-07-2013, 11:04 PM   #9
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Quote:
Originally Posted by jmfitzgerald
great thanks! this is all great info, guess i should of researched a bit more before getting the refractometer... but either or, it's another good tool to have, and i learned something new.

where i thought it would be great is checking the gravity along the aging process. i've been doing quite a few small 1 gallon batches, and was thinking less of contamination, oxidation, etc by taking a couple small drops of the mead out vs taking out a big enough sample to float a hydrometer in, then returning that sample. again because of the small batches, or i'd have no mead left and tons of head space in the carboy but i guess i'll keep sanitizing everything all the time and so far so good!

thanks again, these forums are great!
Once I figured out YE calibration for fermented wort I've been pretty happy with the refractometer. Mine seems to work well for home brewing, and it's a heck of a lot easier than the hydrometer. I own beersmith and bought the iPhone app - both have a refractometer conversion tool.

Note that you also have to check the calibration on hydrometers (and thermometers) every once in a while. Having ATC (auto temp control) makes my life much easier.
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Old 01-08-2013, 12:06 AM   #10
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Quote:
Originally Posted by Devo9
I am wondering, has anyone tried measuring the specific gravity of pure honey with a refractometer before? Would that work?
Most refractometers used in brewing max out at about 32 Brix, most honey is about 82 Brix. Therefore you can't measure the honey straight. You can however dilute the honey with water, a ratio of 3:1 or 4:1 hot water to honey should work. Just multiple the reading by the ratio (e.g. A reading of 21 Brix in a 3:1 solution would mean the honey is actually 84 Brix.)


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